Rechargeable lithium batteries which are attractive as power sources for portable electronics, use organic electrolyte, and exhibit twice the discharge capacity of conventional batteries with an alkaline aqueous electrolyte solution while exhibiting high energy density.
Positive active materials use oxides of lithium and transition metals having a structure capable of intercalating lithium. Examples include LiCoO2, LiMn2O4, and LiNi1−xCoxO2 (where 0<x<1).
Attempts have been made to use lithium metal as a negative active material for rechargeable lithium batteries because of its high energy density. However, lithium metal causes serious problems with dendrite formation on the surface of the lithium metal during charging and discharging. This may cause a short circuit and may further increase the reactivity of the lithium metal so that the lithium metal reacts with the electrolyte to form a polymer film without ionic conductivity on the surface of the lithium metal. As a result, the battery resistance increases abruptly, preventing smooth charging and discharging.
Such problems have been addressed by replacing lithium metal with carbonaceous materials which are capable of intercalating and detintercalating lithium ions. Carbonaceous materials have no shortcomings associated with dendrites and have advantages such as good voltage flatness and relatively good cycle life characteristics. However, such carbonaceous materials tend to be highly-reactive with organic electrolytes, exhibit low power as a result of the slow diffusion rate of lithium in the material, tend to have initial irreversible capacity, and batteries made from such materials can exhibit high volume expansion or swelling.
The shortcomings are more complicated for carbonaceous materials than for lithium metal. Thus, attempts to return to the use of lithium metal by addressing dendrite formation and giving prolonged cycle life characteristics have attracted attention. One approach is found in U.S. Pat. No. 6,051,340 which discloses a negative electrode including a metal capable of being alloyed with lithium and a metal incapable of being alloyed with lithium. The metal incapable of being alloyed with lithium acts as a current collector, and the metal capable of being alloyed with lithium forms an alloy with lithium ions released from a positive electrode during charging. The alloy acts as a negative active material and the negative electrode includes lithium during the charging.